While about 30,000 Americans are afflicted with cystic fibrosis, the FDA-approved Kalydeco only treats the 4 percent of the population that suffers with a rare form of the illness.

"Even though this drug isn't for the majority of people, it proves that you can look at the mistake in the genes and design a drug in a rational way that will fix the problem," said Dr. Drucy Borowitz, at the State University of New York at Buffalo, where she directs the cystic fibrosis program.

The disease causes sticky mucus buildup in the lungs and other organs, leading to infections, digestive problems, and death in young adulthood.

Currently Kalydeco is approved for patients 6 years old and up. But Vertex Pharmaceuticals Inc., the drug's maker, is planning to study the drug in patients as young as 2 years old. The hope is that early use of the medication will prevent permanent lung damage.

Researchers also hoped it will eventually help the rest of those who suffer from the more common form of the genetic disease.